Game concept
Mitigate Infirmity
From the game's encyclopedia
Staying healthy is the main way to stave off infirmity.
The Infirm Trait progresses by a full level when contracting an Illness, and by a small amount every year.
If you are sick for a prolonged amount of time, the Trait Path will progress much faster each year. It will also progress much faster if you're more than 65 years old.
The game's text for patch 1.20.1.2. Words in blue are entries of the encyclopedia: hover one to read it, as in the game.
Mitigate Infirmity is an entry of Crusader Kings III's in-game encyclopedia. The game explains it: "Staying healthy is the main way to stave off infirmity." It is part of Elder Health Traits. Patch 1.20.1.2, from game/common/game_concepts/00_game_concepts.txt and game/localization/english/game_concepts_l_english.yml.
Source: game/common/game_concepts/00_game_concepts.txt, game/localization/english/game_concepts_l_english.yml and the English localisation, Crusader Kings III 1.20.1.2.